This invention concerns pipe joining methods, and particularly the joining of pipe ends in the fabrication of various types of pipelines, primarily in well drilling and casing in the oil and gas industry and in pipelines.
Pipe joints most commonly involve threaded coupling or end fittings. When deep drilling of wells, the pipe sections become progressively smaller in diameter due to the techniques which are employed for deep drilling. In order to increase flow from the wells the liners and casings are expanded in place in order to get a larger flow from the well. Threaded joints prevent getting a larger flow from the well. Threaded joints prevent mechanical expansion of the joints and create other problems. Another method for connecting tubular elements, such as pipes is known that provides for formation of external features on the pipe ends to be joined and crimping by plastic deformation of the female part over the male part, with formation of a multi-faceted mating surface that features a beaded collar to ensure higher strength.
This method is described in USSR Inventor's Certificate no. 603,470.
The deficiency of that method is that it is limited to connecting pipes of different diameters and requires considerable labor-intensive preparation (processing) of the ends of the pipes to be joined.
A method for connection of pipes of identical diameters is also known that features forming thicker ends of the pipes to be joined, combined with an increase in outside diameters, without altering the internal diameters to be used for joining of pipes as by welding, brazing and/or bolting.
This method is described in USSR Inventor's Certificate no. 1,703,224.
The deficiency of that method lies in the fact that there is a wall thickening in the pipe joint that makes it difficult to expand the pipe in order to increase the internal diameter of the pipes joined. This method cannot be used, for example, in the oil and gas industry for expansion of pipes in order to increase capacity such as for oil well casings.
Yet another known pipe joining method features a preliminary deformation of the mating pipe ends, assembly by inserting one pipe into the other along mating surfaces, followed by radial crimping along the entire connection length by pushing the joint section through a tapered die.
This method is described in U.S. Pat. No. 4,026,006.
The deficiency of that method arises from the lack of a tight fit between the mating surfaces of the pipes being joined such that it does not ensure leakproof joints along its entire length. Elastic relief of the pipe ends at certain sections of the joint may result in formation of a gap along the mating surfaces.
Furthermore, the pipe overlaps in the joint results in a double or almost double wall thickness and while this increases the joint strength, it also makes pressure expansion of the joined pipes problematic.
An object of the present invention is to assist in the deformed expansion of pipes in oil and gas wells and in other applications to provide an equal expansiveness of joined pipes in the joint and the rest of the pipe sections to allow deformation by a subsequent expansion of the joined ends of the pipes by maintaining the original O.D. and I.D. of the pipe ends in the pipe joint and improving the leakproof performance of the pipe joint by an interference fit of the mating pipe surfaces.